There are a number of non-resorbable, particle-based compositions used for permanent correction or augmentation of soft tissue defects or augmentation for cosmetic purposes. Each composition is associated with certain advantages and disadvantages. Silicone gel was frequently used to treat dermal defects, such as wrinkles, folds, and acne scars in the 1970's and 1980's but has since been prohibited from use in these applications. Silicone was frequently associated with chronic inflammation, granuloma formation, and allergic reactions. TEFLON® paste is a suspension of polytetrafluoroethylene particles in glycerin. This composition was primarily used for vocal fold augmentation and has been associated with granuloma formation. Bioplastics composed of polymerized silicone particles dispersed in polyvinylpyrrolidone. This composition has been withdrawn from commercial application due to frequent chronic inflammation and
tissue rejection. Polymethylmethacrylate (PMMA) microspheres having a diameter of 20-40 μm and suspended in a bovine collagen dispersion have been described by Lemperle (U.S. Pat. No. 5,344,452). Since the composition contains collagen from a bovine source, skin testing is required. In addition, the composition is associated with sterilization challenges; the bovine collagen dispersion is damaged by standard terminal sterilization techniques, including heat and gamma irradiation. PMMA is also labile to heat sterilization conditions.
Carboxymethylcellulose and other polysaccharides are examples of material used in gel or solution form for a variety of medical and non-medical applications. Sodium carboxymethylcellulose (“CMC”) is cellulose reacted with alkali and chloroacetic acid. It is water soluble and biodegradable and used in a number of medical and food applications. It is also commonly used in textiles, detergents, insecticides, oil well drilling, paper, leather, paints, foundry, ceramics, pencils, explosives, cosmetics and adhesives. It functions as a thickening agent, a bonder, stabilizer, water retainer, absorber, and adhesive.
The prior art gel materials teachings treat the gel merely as a carrier, incidental to the actual augmentation function of the gel; and there has been no directed effort to understanding how best to prepare an implant which is truly compatible rheologically and chemically with an implant site. Further, conventional methods and products fail to address several problems with current gels. More specifically, the injectable materials of the prior art fail to address the specific difficulties in applying implants across a wide range of locations in the body and consequently fail to provide the appropriate type of implant. For example, current implants can experience occlusion, or irregular implantation during the implantation procedure when a fine gauge needle is used. While in certain applications a fine gauge needle may not be required, it is vital to the success of several applications. In addition, a smaller gauge needle leaves a smaller puncture point, which is often desirable to patients. Furthermore, the propensity for occlusions often results in uneven, erratic and discontinuous implantation, which causes highly undesirable results.
In another aspect of conventional methods and products, current implants have failed to address the viscoelastic properties of the implant in the syringe, such that current implants require a significant amount of force, and even irregular levels of force, to extrude the implant from the needle, much more so as the needle gauge is reduced. This presents fatigue issues for medical professionals who may well be performing many injections in a day. This also makes any given injection more difficult to perform, and also perform proper injection amounts and distributions, because of the necessity to exert a large amount, or an irregular amount of force on the syringe, while maintaining a steady needle during injection.
Conventional methods and current implant materials also fail to address the wide range of distinctions in the different tissues in which the implants are placed. Implants can undergo unwanted agglomeration, chemical reaction, phase separation, and premature breakdown of the implanted mass into discontinuous variable shapes, all of which can consequently manifest different undesirable mechanical properties and performance relative to the implant tissue region.
Material composition and its associated mechanical, chemical, and even electrical and other physical properties are important relative to: compatibility and stability at the tissue implant site; controlled and proper tissue in-growth and to implement integration into the tissue, immuno-histo tissue response, and mechanical and visual appearance. The augmentation performance for the patient encompasses proper aesthetic outcome arising from the function of the physical components and the chemical composition of the composite of gel and particles implant. In particular, prior art implants utilizing gels have relied on the gel as a carrier but have failed to recognize and solve the problem of providing an implant with a gel which is designed to cooperate with the solid particles to mimic, both mechanically and chemically, the tissue into which it is injected and to behave in a symbiotic controlled manner when embedded in the tissue.
Implants using prior art gels exhibit a tendency to form nodules, or to migrate from the desired implantation location, or to undergo unwanted and undesired chemical and/or mechanical breakdown, such as phase separation or formation of unwanted geometries and cosmetic appearance in the body. None of these is an acceptable result for a patient. Nodule formation has been previously reported for known compositions by M. Graivier and D. Jansen, “Evaluation of a Calcium Hydoxylapatite-Based Implant (Radiesse) for Facial Soft-Tissue Augmentation,” Plastic and Reconstructive Surgery Journal, Vol. 118, No. 3s, pg. 22s (2006).